Bond dissociation & electronegativity equalization

It is well known that the Electrongativity Equalization Mtehod (EEM) fails to describe the charge distribution upon bond dissocation. In this presentation, the bond dissocation is studied with the Atom-Condensed Kohn-Sham DFT approximated to second order (ACKS2). After reviewing the basic equations, a two-fragment system is studied in the dissociation limit. The limiting behavior of the Coulomb interaction (1/r) and the Kohn-Sham matrix elements (exponentially decaying) are plugged into the equations. The solution exhibits integer dissocuation limits, in line with high-level ab initio computations. A direct fit of the ACKS2 model to reproduce constrained CAS-SCF reference data yield parameters that are in line with experimental atomic data.